Piston



A. W. POPt 1R.

PISTON.

APPLICATION FILED FEB. 21, 1921.

Patmted 0115 241 1922 Patented Get. 24, 1922.

UNHTED stares ARTHUR W. POPE, JR., 0F KENOSHA, WISCONSIN.

PISTON.

Application filed February 21, 1921.

To all whom it may concern:

Be it known that I, ARTHUR W. Porn, J12, a citizen of the United States, residing at Kenosha, in the county of Kenosha. State of Wisconsin, having invented certain new and useful Improvements in Bistons, do hereby declare that the following is a full, clear, and exact description of the same.

The invention relates to pistons for internal combustion engines, and consists of the matters hereafter described and particularly pointed out in the appended claims.

In the accompanying drawings Figure 1 is a view showing a central vertical section through a cylinder and a piston embodying the features of my invention; Fig; 2 is a sectional view of the piston on the line 2--2 of Fig. 1 the split piston ring being omitted,

and Fig. 3 is a sectional view on the line 3+3 of Fig. 1.

Referrin to the drawings, 1 designates the wateracketed cylinder of an internal combustion engine of any suitable construction, while the piston is of the hollow trunk type comprising a head 2 and a skirt 3, the head being provided with the usual circumferential grooves for the split piston rings 4, and the inner surface of the skirt being provided at diametrically opposite points with the usual bosses 5 to receive the crankpin of a connecting rod (not shown), the construction so ,far described being typical of the conventional automobile engine.

It is a matter of common knowledge that in the operation of internal combustion engines great pressure is created in the cylinder above the piston on the compression stroke of the piston and is enormously increased on its expansion stroke upon explod. ing the compressed charge, and that consequently gas-tight conditions are necessary between the cylinder and piston. Otherwise the gas or vapor escapes between the piston and cylinder, so that on the compression stroke of the piston there is consequent loss of compression and so diminution of the full power volume of the charge as the latter depends on complete combustion of the charge which in turn depends on perfect compression, and on the explosion stroke there is also loss of power by the fuel escaping past the piston instead of having its expansive force confined above the piston head; also. among further objections, such fuel as leaks by the piston dilutes the engine oil in the crank chamber,

Serial No. 446,830.

and an excess of lubricating oil produced in the film between the piston and cylinder by excessive clearance causes carbon in the cylinder with its known objections. On the other hand, it is necessary to use pistons of sufficiently reduced diameter to provide clearance for free play between the iston and cylinder to allow for the expansion of the iston caused by the high temperature of t e exploding charges and prevent it from binding or sticking both before the cylinder wall becomes heated and after it becomes heated as these parts do not expand equally as their temperatures are not always the same. When the piston and cylinder have substantially the same co-ofiicient of expansion their tendency to unequally expand is reduced to the minimum, but as the cylinders are usually made of cast-iron the weight of the pistons when made of the same material has proved disadvantageous and objectionable, and on the other hand when it was sought to overcome this latter objection by making the pistons of lighter material, such for example as an aluminum alloy, the comparatively high coefficient of expansion of its material caused the piston when heated to bind on the cylinder under normal clearance or necessitated an excessive amount of clearance between the piston and cylinder with a consequent loss of compression and power. as well as other objections. I

In order to materially lighten the Weight of the piston and at the same time to compensate for the comparatively higher co-efiicient of expansion ofa metal prmiding such decreased weight. I pron'de a piston composed of a metal lighter and of a higher coefiicientof expansion than the metal of the cylinder and having rings of the same co efiicient of expansion as the cylinder so arranged that the efi'ective diameter of the piston is approximately the same as that of a piston made of the same metal as the rings, and the lighter piston fits the cylinder with the usual clearance but with entire freedom from sticking.

Tn carrying out my invention, assuming that the cylinders areof cast-iron as in the conventional automobile engine. I make the head and skirt of the piston of metallic material lighter than the cylinder. preferably using any well-known aluminum alloy. for example that commercially known as lynite. and this piston is slitted in several places to give it flexibility and is provided with rings having substantially the same coefiicient of expansion as the cylinder, one of the rings retarding the expansion of the piston and the other preventing the contraction of its skirt. In practice the piston is slitted longitudinally in several places, in the present embodiment four such slits 6 being shown, and these slits extend through the piston from a point in the head down through the skirt to its lower end. The head is also provided with a series of circumferential slits 7, extending through its wall and preferably located one at the upper end of each of the longitudinal slits 6. These slits give flexibility to the piston; the circumferential slits 7. which in practice are equal in length to about one twelfth the circumference of the head, provide increased flexibility between the head and sections of the-skirt to permit the diameterof the head to expand to a greater amount than the diameter of the skirt: and the longitudinal slits 6 allow the divided portions or sections of the skirt to open and close radially.

A pair of closed rings or bands 8 and 9, of the same coefiicient of expansion as the cylinder wall. are arranged on the piston to make its effective diameter approximately the same as that of a piston made of the same metal as the rings themselves. In the usual practice these rings are made of cast iron, corresponding to the metal of the cylinder. The lower ring 8 is sprung into a groove on the inside of the skirt near its bottom as indicated. the sections springing apart to allow the ring to be inserted. This provides primarily for adjustment of the diameter of the skirt by the use of different sized rings, and ring gives rigidity and prevents the piston from contracting or being compressed at the bottom. The upper ring 9 is placed slightly below the upper end of the slits 6 on the outside of the piston as indicated: it is closed or made continuous by brazing, welding or other suitable method. This ring 9 retards the expansion of the piston. and restrains it from expanding beyond the expansion of the ring itself. It furthermore serves as a very desirable bearing surface at the upper end of the piston. As is the usual practice the circumference of the head is reduced to fit loosely in the cylinder. and so all bearing between the cylinder wall and piston occurs on this ring or on the portion of the piston wall which is below this ring. it is apparent therefore that the diameter of the piston at any point below this ring cannot expand a greater amount than the ring itself. and when heat is applied to the piston it will expand approximately the same amount as a piston made of the same metal as the ring. The effective diameter of this piston is approximately the same as the diameter of a piston made en.-

tirely of the same metal as the rings, assuming that the two pistons are used and operated under like conditions. A piston constructed as above described obviates the difiiculties heretofore attendant upon the use of aluminum pistons in automobile engines due to the comparatively high coeflicient of expansion of the aluminum which makes it necessary to allow an excessive amount of clearance between the piston and the cylinder wall, and makes it possible to fit an aluminum piston with the same clearance as used with a cast iron pistonin the cylinder of the conventional automobile engine.

A piston made as above described from lynite, an aluminum alloy, with the rings 8 and 9 made of cast iron, the top ring being split, sprung into position and then brazed, and the bottom ring made continuous and snapped into position, was fitted into a conventional cast iron cylinder of an automobile engine with 2% inch bore, a clearance of 0.0025 of an inch being allowed, and this piston operated satisfactorily at all speeds and both when the engine was cold and after it had run sufliciently long to become thoroughly heated. As the expansion of the piston is restrained by the outer ring, and the internal ring merely provides for adjustment of the diameter of the skirt and prevents contraction of its lower portion it is not necessary in providing for expansion clearance between the piston and cylinder to use an inner ring having a lower co-efficient of expansion than the material of the piston.

Furthermore, by using rings of different radial thickness, or byinserting thin shims or strips of metal between the rings andpiston, it is possible to change the effective diameter of the piston to compensate for wear of the cylinder walls after long use.

A piston constructed according to my invention is useful and advantageous in other relations, for example in a high speed compressor or pump.

I claim:

1. In combination with a cylinder of an internal combustion engine. a piston comprising a head and a skirt formed of metal having a higher co-eliicient of expansion than the cylinder. a closed ring seated in the outer surface of the head and forming a bearing surface for the upper end of the piston, and a second closed ring seated in the inner surface of the skirt near its bottom, said rings formed of metal of substantially the same co-eflicient of expansion as the cylinder.

2. In combination with a cast-iron cylin der of an internal combustion engine, a piston comprising a head and a skirt of alurninum alloy. said head having circumferential slits. and said skirt and head having longitudinal slits, a cast-iron closed ring seat d in the-outer surface of the head, and a castiron closed ring seated in the inner surface of the skirt near its bottom.

3. A piston for internal combustion engines comprising a head and a skirt of aluminum alloy, said head having circumferential slits and a groove in its outer surface below said slits. said skirt and head having longitudinal slits extending from the circumferential slits through the bottom edge of the skirt, said skirt also having an inner groove near its bottom, a cast-lron ring in said outer groove, and a cast-iron ring in said inner groove.

4. A piston for engine cylinders comprising a head and a skirt of metal having a higher co-eflicient of expansion than the cylinder, said head having circumferential slots, and said skirt having longituinal slots, and a closed ring having a lower co-efiicient of expansion than the piston seated on its outer surface below the upper ends of the longitudinal slots.

5. A piston for engine cylinders comprising a head and a skirt of aluminum alloy. said head having circumferential slots. and said skirt having longitudinal slots, and a closed ring havlng a lower co-eflicient of expansion than the piston seated on its outer surface below the upper ends of the longitudinal slots to restrain the expansion of the skirt.

ARTHUR W. POPE, J R. 

